How to change 3 Ph supply frequency?

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Discussion Overview

The discussion revolves around methods to change the frequency of a three-phase power supply smoothly over a wide range (1Hz to 100Hz), specifically focusing on solutions that do not involve variable frequency drives or motor-generator sets. Participants explore various approaches and express concerns about the feasibility of different methods.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests synthesizing three sinusoids from DC using semiconductor circuits, referred to as a function generator, for low power applications.
  • Another participant questions the relevance of low power applications, emphasizing the need for clarity on the power levels involved.
  • Some participants mention the use of high power AC-DC-AC power links as a reference for changing frequency, but express uncertainty about the specifics of the application.
  • Concerns are raised about the practicality of achieving low frequencies, such as 1Hz, with large generators, which would be required for high power applications.
  • There is a suggestion that direct conversion of frequency may not be possible without going through a DC stage, although this remains uncertain.
  • Participants seek further clarification on the power requirements and the specific industrial applications that necessitate such frequency changes.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the methods to change the frequency of a three-phase supply, with multiple competing views and uncertainties regarding the feasibility and practicality of the proposed solutions.

Contextual Notes

The discussion highlights limitations in specifying power levels and the challenges associated with achieving low frequency outputs in high power applications. There is also ambiguity regarding the direct conversion of frequency without intermediate steps.

bobby2211
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Hello,

I would like to know about, How to change the 3 Phase supply frequency smoothly over a wide range(for example 1Hz - 100Hz)?

suggest methods if any exists other than mentioned below :
1)Not using Variable frequency drives
2)Not using MG set

Pl note that i want to know, how to change 3 phase supply frequency, not at the generation side.

Thanks.
 
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If you are talking low power (e.g., to power an experimental design) then you could synthesize three sinusoids from DC using semiconductor circuits, where it's called a function generator. Quite possibly a stepped approximation to a true sine wave would suffice.
 
NascentOxygen said:
If you are talking low power (e.g., to power an experimental design) then you could synthesize three sinusoids from DC using semiconductor circuits, where it's called a function generator. Quite possibly a stepped approximation to a true sine wave would suffice.

No its not for experimental use.

And i have clearly mentioned, that i want to know, how to change 3 phase supply frequency?
So do u have any other options for the above question?
 
See how it's done at either ends of high power AC-DC-AC power links (e.g. UK link with the French network). Or perhaps you are only concerned with relatively low powers. The actual spec would be vital to consider before making a choice.
 
sophiecentaur said:
See how it's done at either ends of high power AC-DC-AC power links (e.g. UK link with the French network). Or perhaps you are only concerned with relatively low powers. The actual spec would be vital to consider before making a choice.

Why you talk about low power application?

Yes, i can change 3 phase supply frequency using Motor generator set. Where generator rotor runs at Nr to obtain desired 'f'.
But i don't want to implement it as it is a cumbersome process.

so is there any other method to change supply frequency smoothly?
 
bobby2211 said:
No its not for experimental use.

And i have clearly mentioned, that i want to know, how to change 3 phase supply frequency?
So do u have any other options for the above question?
May I ask what the industrial application is where you know of a need for this?
 
bobby2211 said:
Why you talk about low power application?

Yes, i can change 3 phase supply frequency using Motor generator set. Where generator rotor runs at Nr to obtain desired 'f'.
But i don't want to implement it as it is a cumbersome process.

so is there any other method to change supply frequency smoothly?

You didn't make clear what power you are considering.
I did not suggest a motor generator solution - how would you do that for a 1Hz supply? The generators would need to he MASSIVE.
I was suggesting MAR technology. But 1Hz is an unrealistic suggestion for motors or inverters.

You will not find a system for direct conversion. It will be necessary to go via DC, I am sure.
You still do not specify the Power involved. Is it a secret?
 
sophiecentaur said:
You didn't make clear what power you are considering.
I did not suggest a motor generator solution - how would you do that for a 1Hz supply? The generators would need to he MASSIVE.
I was suggesting MAR technology. But 1Hz is an unrealistic suggestion for motors or inverters.

You will not find a system for direct conversion. It will be necessary to go via DC, I am sure.
You still do not specify the Power involved. Is it a secret?

Firstly i would like thank you for patiently replying to my post.

It deals with high power AC sources.

Yes, that is what i want to perform. i.e. will i be able to convert 50hz 3 ph supply to 1Hz 3 phase supply or 51 or vary smoothly over a range?

Yes you are right generators are massive and i don't prefer them too.

So u say that direct conversion is not possible? or Do u have any idea about direct conversion?

And there is no secret involved my friend and there's nothing to reveal.

Finally it will be helpful if u can give me some more suggestions.
 
What do you call "High Power" exactly?
10kW
1MW
1GW
??

I can't think of may applications that would require enormous powers at a few Hz. What would you do with 1MW at 1Hz?
Inductances would need to be massive, in any AC equipment - either for generation or use.
 

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